Multiple shaft engine

ABSTRACT

An internal combustion reciprocating engine including a drive shaft, at least one piston, and a piston coupling corresponding to each piston wherein each coupling includes: a crank rotatably coupled to the piston, a first and second toothed crank cam gear fixedly coupled to the crank, a first and second complementary toothed drive cam gear fixedly coupled to the drive shaft and drivingly engaged with the corresponding first and second crank cam gears for at least a first and second portion, respectively, of a complete revolution of the drive shaft so linear movement of the piston is converted to rotation of the drive shaft.

FIELD OF THE INVENTION

This invention relates to a mechanism for application to internalcombustion engines.

The mechanism concerns a piston and drive shaft coupling. The couplingcommunicates energy from the piston to an engine's drive shaft in amanner that permits the piston to move in a predetermined characteristicdifferent from the generally sinusoidal characteristic resulting from aconventional piston coupling.

This mechanism may be applied to either a two-stroke or four-strokeinternal combustion engine.

BACKGROUND

It is known in multi-cylinder internal combustion piston engines toprovide a single crankshaft to which each piston is attached by means ofa connecting rod. When the crankshaft is rotating at constant speed,each upstroke and downstroke of the piston has the same duration. Themovement of each piston is characterised approximately by a sine wavewhich indicates the position of the piston in the cylinder as a functionof the rotational position of the drive shaft.

It is desirable for a number of reasons including optimising combustionefficiency, increasing fuel economy, maximising power output, increasingtorque, reducing mechanical stresses, or generally enhancing tuningflexibility to be able to modify the characteristic relationship betweenthe motion of the piston and the drive shaft. Hitherto, attempts to dothis have been largely unsuccessful.

It is an object of the present invention to overcome or substantiallyameliorate one or more of the disadvantages of the prior art, or atleast to provide a useful alternative.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided aninternal combustion engine including:

a drive shaft;

a crank including a crank pin;

a piston mounted for reciprocation within a cylinder;

a connecting rod extending between the piston and the crank pin;

a first crank gear mounted on the crank; and

a first drive gear mounted on the drive shaft;

wherein the first crank gear and the first drive gear form a first gearpair;

wherein said first gear pair is drivingly engaged for at least a firstportion of a complete revolution of the drive shaft; and

wherein at least one of the first crank gear and the first drive gear ofsaid first gear pair is non-elliptical;

such that reciprocation of the piston causes rotation of the drive shaftin a relationship determined by the respective profiles of the crankgear and the drive gear of the first gear pair.

Preferably, the first drive gear and the first crank gear have an equalnumber of teeth so that one revolution of the crank gear produces onerevolution of the drive shaft. Preferably also, the crank gear and thedrive gear are both non-elliptical.

In one preferred embodiment, one or other of the drive gear and thecrank gear is eccentrically mounted to the drive shaft or the crankrespectively. Alternatively, both the drive gear and the crank gear maybe eccentrically mounted. In a preferred form, the crank gear isintegral with the crank.

In another preferred form, the engine further includes:

a second crank gear mounted to the crank; and

a second complementary drive gear mounted to the drive shaft;

wherein said second crank gear and second drive gear form a second gearpair;

wherein the second gear pair is drivingly engaged for at least a secondcomplementary portion of a complete revolution of the drive shaft; and

wherein at least one of the second crank gear and the second drive gearof said second gear pair is non-circular;

such that reciprocation of the piston causes rotation of the drive shaftin a relationship determined by the profiles of the crank gears and thedrive gears of the respective first and second gear pairs.

More preferably, the first and second crank gears are different incircumferential length. The first and second drive gears are preferablyformed as a single composite gear having a first portion engaged withthe first crank gear for the duration of one complete revolution of thecrank, and a second portion engaged with the second crank gear for theduration of a subsequent complete revolution of the crank, therebyproviding one drive shaft revolution per two crank gear revolutions.

Still more preferably, the crank gear and the drive gear of each gearpair are both non-circular. In other preferred forms, one or both of thegears of each gear pair are eccentrically mounted respectively to theirdrive shaft or crank.

In a further preferred form, the engine includes a plurality of pistonsand a single drive shaft, wherein each piston has an associated crankincluding a crank pin, a connecting rod extending between the piston andthe crank pin, a first crank gear mounted to the crank and a first drivegear mounted to the drive shaft.

Still more preferably, all of the respective cranks are joined by asingle crankshaft having a plurality of crank pins.

DRAWINGS

A preferred embodiment of the invention will now be described, by way ofexample only, with reference to the following drawings in which:

FIG. 1 illustrates a front view of a two stroke internal combustionengine in accordance with the invention;

FIG. 2 illustrates a partially cut away view of the engine of FIG. 1;

FIG. 3 illustrates a partially cut away rear view of the engine of FIGS.1 and 2;

FIG. 4 illustrates a partially cut away side view of the engine of FIGS.1 and 2;

FIG. 5 illustrates a partially cut away side view of the engine of FIGS.1 and 2 opposite to that shown in FIG. 4;

FIG. 6 illustrates a functional view of the operation of the engineshown in FIG. 2 during various instances during a stroke;

FIG. 7 illustrates the piston travel-drive shaft characteristic for botha conventional two stroke internal combustion engine and a two strokeinternal combustion engine according to the invention;

FIG. 8 illustrates an embodiment of a gear pair for an engine inaccordance with the invention;

FIG. 9 illustrates the pitch circumference profile of the gear pair ofFIG. 8;

FIG. 10 illustrates a functional view of an embodiment of some of thecomponents of a piston coupling in accordance with the inventionsuitable for use in a four stroke reciprocating internal combustionengine;

FIG. 11 illustrates a functional view of the operation of the pistoncoupling in FIG. 10 during various instances during a complete fourstroke cycle;

FIG. 12 illustrates a conventional and a selective piston travel-driveshaft characteristic in a four stroke internal combustion engine;

FIG. 13 illustrates a perspective view of an embodiment of some of thecomponents of a piston coupling in accordance with the invention;

FIG. 14 illustrates an alternate perspective view to that shown in FIG.13 during a different instance during operation;

FIG. 15 illustrates an embodiment of some of the components of a pistoncoupling in accordance with the invention;

FIG. 16 illustrates the pitch circumference profile of the components inFIG. 15;

FIG. 17 illustrates a perspective functional view of an arrangement oftwo piston couplings in accordance with the invention suitable for usein a four stroke internal combustion engine; and

FIG. 18 illustrates the perspective view of FIG. 17 viewed from theother side.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 6 illustrate a two stroke internal combustion engine 12according to the invention. Wherever possible, like reference numeralswill be used to indicate like features.

The internal combustion engine 12 includes a drive shaft 7 and a crank26 including a crank pin 40. A piston 27 is mounted for reciprocationwithin a cylinder 1 and a connecting rod 25 extends between the piston27 and the crank pin 40. A first crank gear 21 mounted on the crank 26and a first drive gear 23 is mounted on the drive shaft 7. Optionally,the crank gear 21 can be integrally formed with crank 26 and similarly,the drive gear may be integral with the drive shaft. The gears 21 and 23form a first gear pair. It will be obvious that gear 23 isnon-elliptical. However, in other forms one or the other may beelliptical or circular. It will be appreciated that a circle is aspecial form of an ellipse where the length of the major and minor axesare equal.

The drive gear 23 is engaged with the crank gear 21 such thatreciprocation of the piston 27 causes rotation of the drive shaft in arelationship determined by the profiles of the crank gear and the drivegear. In the preferred form both the drive gear 23 and the crank gear 21have an equal number of teeth 33. Consequently, one revolution of thecrank gear produces one revolution of the drive shaft.

In use, the engine illustrated in FIGS. 1 through 6 can achieve a pistontravel drive shaft characteristic 71 as shown in FIG. 7. The typicalsinusoidal characteristic provided by conventional engines is showngenerally at 70. The particular profile or characteristic achieved by anengine according to the invention, and in practical terms the fashion inwhich linear movement of the piston 27 is converted to the rotation ofthe drive shaft 7, is affected by the selected shapes of the crank gear21 and the drive gear 23. Also, the location at which the gears 21 and23 are mounted to the crank 26 and the drive shaft 7 respectively canaffect the profile achieved.

The particular embodiment shown in FIGS. 1 through 6 includes a crankgear 21 which is generally elliptical in shape. The axis 22 of rotationof the crank passes through crank gear 21 off the centre of the minoraxis of the gear, as best seen in FIG. 8. The minor axis of gear 21 isparallel to the longitudinal centre line of crank 26.

The pitch circumference 91 of non-elliptical complementary drive gear 23is indicated in FIG. 9 as is the pitch circumference 90 of crank gear21. Also, drive gear 23 has the same number of teeth as crank gear 21.Consequently, one complete revolution of crank gear 21 produces onecomplete revolution of the drive shaft 7. The shape of drive gear 23 andthe distance between the axis 22 of rotation of crank 26 and the driveshaft 7 are selectively determined so that gears 21 and 23 complete onerotation simultaneously, even though, at different stages during therotation, the crank 26 will be rotating more quickly or more slowly thanthe drive shaft 7.

Advantageously, the piston 27 will move more slowly in the top deadcentre (TDC) and bottom dead centre (BDC) regions and more quicklyduring a compression stroke when compared to a piston in aconventionally arranged engine. Once again, the profiles 70 and 71indicating the piston travel drive shaft characteristic for conventionalengines and engines according to the invention respectively areillustrated in FIG. 7.

The particular specifications of the crank gear 21 and the drive gear 23are detailed below.

CRANK GEAR 21 SPECIFICATIONS: Shape of Pitch Elliptical Semimajor axis50 mm Semiminor axis 30 mm Pitch Circumference 360 mm CrankshaftPosition 12.68 mm off-center along the semiminor axis Number of Teeth 36Gear Type American Standard Involute System - Stub Tooth Circular Pitch10 mm Pressure Angle 20 degrees Addendum 2.546 mm Dedendum 3.183 mmBacklash 0.5 mm. DRIVE GEAR 23 SPECIFICATIONS: Shape Complement to Crankgear 21 Pitch Circumference 360 mm Number of Teeth 36 Distance betweenCrankshaft and Drive 113.045 mm shaft

A further embodiment of the invention will now be further described, byway of example only, with general reference to FIGS. 10 to 16 inclusive.These figures illustrate another embodiment of the invention in the formof a four stroke internal combustion engine.

Once again, like reference numerals are used to indicate like features.

With reference to FIG. 10, the single cylinder four stroke engineincludes a drive shaft 7 and a crank 26 including a crank pin 40. Thecrank has an axis of rotation 22. A connecting rod 25 extends betweenthe piston 27 and the crank pin 40. In addition to the first gear pair,the engine also includes a second crank gear 21 b mounted to the crank26 and a second complementary drive gear 23 b mounted to the drive shaft7. The second crank gear 21 b and the second drive gear 23 b form asecond gear pair. At least one of the second crank gear and the seconddrive gear is non-circular. Optionally both gears are non-circular.

The first drive gear 23 a and the first crank gear 21 a are engaged fora first portion of each complete revolution of the drive shaft.Similarly, the second drive gear 23 b is engaged with the second crankgear 21 b for a second complementary portion of each complete revolutionof the drive shaft 7. In this manner, reciprocation of the piston 27effects rotation of the drive shaft in a relationship determined by theprofiles of the crank gears 21 a and 21 b and the drive gears 23 a and23 b, of the respective first and second gear pairs. It will beappreciated that in this embodiment, the first crank gear 21 a alsoserves as the crank 26.

This gear arrangement causes linear movement of the piston 27 to beconverted to rotational movement of the drive shaft 7 by at least thefirst gear pair during the first section of each revolution, and by atleast the second gear pair during the second part of each completerevolution, of the drive shaft.

It will be appreciated that crank gears 21 a and 21 b have differentcircumferential lengths. Also, as shown to advantage in FIGS. 11, 13 and14, first and second drive gears 23 a and 23 b have been joined to forma single gear having a first planar portion engaged with the first crankgear 21 a for the duration of one complete revolution of the crank 26and a second planar portion engaged with the second crank gear 21 b forthe duration of a subsequent complete revolution of the crank, providingone drive shaft revolution per two crank revolutions.

It will be readily appreciated from FIG. 10 that the first and secondcrank gears 21 a and 21 b are circular and the second crank gear 21 b iscentrally mounted about the axis 22 of rotation of the crank 26.

The first crank gear 21 a is mounted eccentrically about the axis 22such that its pitch circle 181 touches the pitch circle 180 of thesecond crank gear 21 b at one point as illustrated in FIG. 16. Onefurther point to note with reference to FIG. 10 is that where gears 21 aand 21 b have a common tangent, ie at the extreme left hand side asillustrated in FIG. 10, the teeth 33 of each gear 21 a and 21 b arealigned. The pitch circumferences 181 and 180 of crank gears 21 a and 21b form a continuous and closed curve through a rotation of 720°.

The two circular gears 21 a and 21 b mesh with drive gears 23 a and 23 bwhich, in combination, have a circumference of pitch circle 182 equal tothe sum of the circumference of pitch circles 181 and 180 correspondingto first and second crank gears 21 a and 21 b respectively. The shape ofdrive gears 23 a and 23 b and the distance between the axis 22 and driveshaft 7 are selected by the requirement that two cycles of the piston 27will result in one complete rotation of the drive shaft 7. This conceptis illustrated in FIG. 11. The piston travel drive shaft characteristic141 of a four stroke engine with the configuration described above iscompared to the characteristic 140 of a conventional four stroke enginein FIG. 12.

The properties and dimensions of crank gears 21 a and 21 b drive gear 23a and 23 b and the gear teeth 33 are tabulated below.

Crank gear 21a Shape Circular Pitch Radius 45.84 mm Pitch Circumference288 mm Crankshaft Position 22.92 mm off center Number of Teeth 36Crankshaft Length 48 mm (Distance between the centers of crankshaft 22and the connecting rod journal) Crank gear 21b Shape Circular PitchRadius 22.92 mm Pitch Circumference 144 mm Crankshaft Position centerNumber of Teeth 18 Drive gear 23a Part 16: Shape Open ovate Pitch Length288 mm Number of Teeth 36 Drive shaft Radius 19.2 mm Drive gear 23bShape Circular arc Radius 88.02 mm Center Center of drive shaft 22Number of Teeth 18 Pitch length 144 mm Center Distance 97.01 mm (Betweencrank shaft 22 and drive shaft 7) Gear Teeth 33 Type American StandardInvolute System - Stub Tooth Circular Pitch 8 mm Pressure Angle 20degrees Addendum 2.0368 Dedendum 2.5464 mm Backlash 0.4 mm

The use of the gear arrangement illustrated in FIGS. 10 through 16 mayallow the relative duration of the power stroke in a four stroke engineto be modified when compared to the duration of the remaining threestrokes.

FIGS. 17 and 18 illustrate a two cylinder engine according to theinvention. In these figures, the features of the engine related to thesecond cylinder are denoted with a prime symbol, eg 23 a′. However,there is only one drive shaft 7 and each of the drive gears 23 a, 23 band 23 a′ and 23 b′ are fixed the drive shaft to provide selective phaseor timing operation of piston 27 in relation in relation to piston 27′.It will be readily appreciated that such an arrangement may be extendedto engines having more than two cylinders.

It will also be apparent that differently shaped crank gears and drivegears to those illustrated herein will provide alternative piston traveldrive shaft characteristics which may be desirable for alternativeapplications. For example, it may be advantageous to slow the pistondown when it is at the top of the drive stroke to allow more time forcombustion under high pressure or, at the bottom of the intake stroke toallow more time for intake of air into the cylinder.

Although the invention has been described with reference to particularexamples, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms. For example, the crankand drive gears may not directly mesh but could alternatively bedrivingly connected by a chain, a pulley, a toothed belt or anintermediate gear train.

What is claimed is:
 1. An internal combustion engine including: a driveshaft; a crank including a crank pin; a piston mounted for reciprocationwithin a cylinder; a connecting rod extending between the piston and thecrank pin; a first crank gear mounted on the crank; a first drive gearmounted on the drive shaft; a second crank gear mounted to the crank;and a second complementary drive gear mounted to the drive shaft;wherein the first crank gear and the first drive gear form a first gearpair; wherein the first gear pair is drivingly engaged for at least afirst portion of a complete revolution of the drive shaft; wherein atleast one of the first crank gear and the first drive gear of the firstgear pair is non-elliptical, wherein reciprocation of the piston causesrotation of the drive shaft in a relationship determined by therespective profiles of the crank gear and the drive gear of the firstgear pair; wherein the second crank gear and second drive gear form asecond gear pair; wherein the second gear pair is drivingly engaged forat least a second complementary portion of a complete revolution of thedrive shaft; and wherein at least one of the second crank gear and thesecond drive gear of the second gear pair is non-circular, whereinreciprocation of the piston causes rotation of the drive shaft in arelationship determined by the profiles of the crank gears and the drivegears of the respective first and second gear pairs.
 2. The engine asclaimed in claim 1, wherein the first and second crank gears aredifferent in circumferential length, and the first and second drivegears are formed as a single composite gear having a first portionengaged with the first crank gear for the duration of one completerevolution of the crank, and a second portion engaged with the secondcrank gear for the duration of a subsequent complete revolution of thecrank, providing one drive shaft revolution for every per two crankrevolutions.
 3. The engine as claimed in claim 1, wherein the crank gearand the drive gear of each gear pair are both non-circular.
 4. Theengine as claimed in claim 2, wherein at least one gear of each gearpair is eccentrically mounted.
 5. The engine as claimed in claim 2,wherein both gears in each gear pair are eccentrically mounted.